The present invention relates to passive heat transfer devices and more particularly relates to two-section heat pipes, which are used in conjunction with a separate air conditioner evaporator, to transfer very high heat fluxes without the addition of external energy.
So-called heat pipes are well known, and typically comprise a condenser and an evaporator connected to one another as a closed system.
Referring now to FIGS. 1 and 2, it has been proposed to reduce the fabrication and installation costs of heat pipes by utilizing U-shaped heat pipes connected to form serpentine heat pipes. Fabrication costs are decreased through the use of the U-shaped tubes. However, it was thought that the serpentine coils would inhibit fluid movement through the heat pipes, thus decreasing their efficiency. One way that such serpentine heat exchangers are rendered useful as heat pipes is to vertically orient a heat exchanger such that the tops of individual coils act as condensers and the bottoms act as evaporators. The individual coils are manifolded together to provide what was thought to be the interconnections required to enable charging all the pipes at once. Thus, referring to FIG. 1, the ends of the individual U-tubes 30A of a heat pipe are manifolded in such a way that the liquid refrigerant can move freely from tube to tube, thus assuring that the liquid level 34A is the same in all tubes. More specifically, the bottoms of the U tubes 35A are pierced and small copper tubes 36A are soldered to the perforations to interconnect the U tubes at their lower ends. The open ends of the adjacent U tubes are manifolded to one another by a straight pipe 37A. The resulting connection allows unrestricted communication between the ends of adjacent tubes and assures that the liquid level is the same in all tubes. Microgrooves 33 are formed in each tube 30A, and the individual tubes are imbedded in aluminum fins 32 to form a heat pipe heat exchanger.
In another configuration utilizing serpentine heat exchangers, two horizontal heat exchangers may be connected to one another such that the lower of the two horizontal serpentine heat exchangers acts as an evaporator and the higher one acts as a condenser. Referring to FIG. 2, it was thought necessary to manifold the U tubes 60A of the lower section by a first copper tube 63A and to manifold the U tubes 61A of the upper section in the same manner by a second copper tube 64A. The upper ends of the thus manifolded tubes are connected by a first copper connection tube 62A which serves as a vapor line, while the lower ends of these tubes are connected by a second copper connection tube 65A serving as a liquid return line.
Each of the devices illustrated in FIGS. 1 and 2 works well. However, both devices are expensive to fabricate and to install, thus rendering them unsuitable for many applications.
It is also known to use heat pipes to increase the dehumidification capacity or efficiency of an air conditioning system. One such system is described in U.S. Pat. No. 4,607,498, which issued to Khanh Dinh on Aug. 26, 1986. Referring to FIG. 3, this type of air conditioning system 110 includes a primary evaporator 124 and a heat pipe heat exchanger 126 which is provided to increase the dehumidification capacity of the system during cool and humid hours. This heat pipe consists of a pair of manifolded heat exchangers of the type illustrated in FIG. 2. A first heat exchanger 128 serves as an evaporator and is located between an inlet of the air conditioner and the primary coil 124. A second manifolded heat exchanger 130 is located between the primary evaporator 124 and the outlet of the housing and serves as a condenser of the heat pipe. The heat sections 128 and 130 are interconnected by a vapor line 134 and a return line 140.
The heat pipe heat exchanger 124 operates as follows:
Warm air enters the housing from the inlet and is cooled slightly as it passes over evaporator 128, thereby vaporizing the liquified refrigerant present in the evaporator. The air then passes over the primary evaporator 124, where it is cooled further. Meanwhile, the vaporized refrigerant rises out of the header of the evaporator 128, through conduit 134, and into the header of condenser 130. The refrigerant in the condenser 130 is cooled by air exiting the primary evaporator 124 so that it is liquefied while simultaneously reheating the air. The liquified refrigerant then flows downwardly into the inlet of evaporator 128 via conduit 140, and the process is repeated.
While the heat pipes described above significantly improve the efficiency of air conditioners, the manifolded heat pipes require additional machining of the serpentine coils and require that headers be connected to the ends of the coils. Accordingly, they are relatively difficult and expensive to fabricate. Thus, the cost of such heat pipes may render impractical their use in many applications, including many conventional air conditioning systems.
In addition, in the air conditioning system described above, the primary air conditioner evaporator 124, the evaporator 128 of the heat pipe exchanger, and the condenser 130 of the heat pipe exchanger, are all manufactured as separate sections. During the assembly of the air conditioning system, the air conditioner evaporator 124 and the heat pipe condenser 130 and evaporator 128 sections are positioned as shown in FIG. 3, and the heat pipe sections are connected to individual end plates which are in turn connected to a housing of the air conditioner system. Alternatively, the heat pipe sections can be connected directly to the housing. Moreover, it is typical for the U-tubes 61A, 60A to be disposed in openings in the end plates or the housing and to be independently expanded in a conventional manner thereby creating a pressurized fit within the end plate openings. The evaporator coils are similarly mounted in the air conditioning system. Once the mounting of the two-section heat pipe and the evaporator is completed, the open ends of the U-tubes 61A, 60A of the two-section heat pipes are connected to manifolds 64A, 65A as shown in FIG. 2, or U-bends 67 as reflected in FIG. 5. The open ends of the evaporator are likewise connected to a common manifold or U-bends. Subsequently, the U-tubes of the two-section heat pipe and of the evaporator are subjected to vacuum and then charged with a refrigerant.
The above-described method of assembly of the heat transfer device within the air conditioning system is very labor intensive, and depending on the design of the air conditioning system, may even be impossible to perform.